This project is part of an integrated approach to use monoclonal and engineered antibodies in radioimaging and therapy of colon cancer. Because of its wide distribution in colorectal tumors, the extensive body of knowledge on its immunology and biochemistry, and the availability of cDNA and genomic clones for CEA and its monoclonal antibodies, the CEA system was chosen for this work. The monoclonal antibody T84.66 which has colon carcinoma specificity and no crossreaction with normal tissue antigens will be used for the imaging and therapy studies. The research goal of this project is to study the antigenic structure of CEA. The antigenic determinant studies will be conducted by expressing CEA in myleoma cells in parallel with Project 3 (expression of immunoglobulins). Since CEA is a member of the immunoglobin supergene family, it is proposed that CEA, portions of CEA, and CEA-Ig fusion products can be expressed to delineate the location of its epitopes. Once the epitope for T84.66 is located, the loop structure will be modeled by molecular graphics in collaboration with Project 3, and the model verified by site-directed mutagenesis. This information will be used to improve the specificity and affinity of Mabs for CEA and other members of the gene family. In addition, this project provides basic immunochemistry and protein studies for the Program. Services include conjugation and testing of antibody-metal ion complexes, quality assurance of radiolabeled Mabs for animal and human use, and structural analysis of recombinant and natural Mabs. The latter work consists of amino acid, microsequence, and FAB/MS analysis. This laboratory also supples expertise in immunoassays and raising monoclonal antibodies.